European Synchrotron Radiation Facility succesfully analyzes zeolites

The structure of zeolite scolecite, showing the aluminium and silicon atoms as the large sphere, connected by oxygen atoms in blue.
Credits: J. Van Bokhoven

June 27, 2008 In a world first, scientists at the European Synchrotron Radiation Facility have determined the distribution of aluminum in zeolites, an important step towards understanding the versatile volcanic material used in water purification, nuclear waste removal, and the spin cycle of your washing machine.

The team, which included researchers from the ESRF, the ETH Zurich, Diamond Light source, the University of Torino, and the University of Hamburg, used the technique of X-rays standing wave to reveal the precise structure of the mineral.

Zeolites are aluminosilicate microporous solids termed “molecular sieves” for their ability to selectively sort molecules. The uniformly arranged pores in zeolites can restrict the passage of neighboring substances, based on size, allowing them to act as molecular filters. This attribute makes zeolites highly suitable for water softening and purification, petrol refinement, the separation of gases, and trapping radioactive ions. However, not all zeolites are involved in such glamorous work – most of the 4 million tons of natural zeolites produced globally per year are incorporated into laundry detergents. A substantial portion of the remainder is used to make concrete, and a large amount of the material has the unenviable fate of being the secret ingredient in unclumping kitty litter.

Facilities like the ESRF are pivotal to improving our understanding of the material so that scientists can reap the full benefits of its vast range of applications. The ESRF is home to the most powerful synchrotron radiation source in Europe, a cyclic particle accelerator that can accurately study chemicals and minerals on a molecular level. Using the sophisticated equipment, scientists were able to chart not only the pore size of scolecite zeolite, but also the location of aluminum within it.

Forty-eight varieties of zeolite are naturally formed in volcanic areas where ash reacts with alkaline groundwater, but more than 150 zeolite types have been synthesized by scientists. While the artificially produced materials are far more pure, the size of the grains are greatly reduced, making effective analysis a harder task. Now that the ESRF has proven successful in analyzing natural zeolites, it is hoped that a comprehensive study of man-made zeolites will follow.

The ESRF’s zeolite research was published in Nature Materials on June 22.